I would desolder the display from the other board.Maybe some text is visible on the bottom of the display pcb.As it's only got 14 pins, and the way it looks to be constructed, the display seems to have no backlight.Try to find indications for pin 1 and for some display manufacturer or the display type.

Have a look at "blink without delay".Did you connect the grounds ?Je kunt hier ook in het Nederlands terecht: http://arduino.cc/forum/index.php/board,77.0.html

You probably do not even have to identify it, just use it with any of the LiquidCrystal example programs.

[Edit] - On second thought you may indeed have to identify it or at least verify the pinout. The devices with pins above the display are pretty standard, the pins are numbered 1 --> 14 starting from the edge of the board. The devices with the pins below the display typically have a non-standard pinout and you may find the pinout reversed, with pin 14 near the edge. Fortunately you do not have to deal with the backlight which would add more uncertainty.

I would start with just the power and GND leads and see what it takes to get a single row of blocks on the screen. Connect +5 to the second pin and connect GND to the first and third pins. If that doesn't work then try again at the other end. I would recommend using a potentiometer to power pin 3 when you actually go to use the device.